The invention relates to an injector used in operations for filling the confined spaces of systems of such types as refrigeration plant, coolant units and others, and for equivalent uses. The injector in question is capable of preventing leaks of pollutant gases from the confined spaces to the external environment, for example and in particular from the dead spaces inside the injector itself, and also of extracting pollutant gases, where necessary, from coolant units which are to be repaired or destroyed. These and other objects of the invention will be clearly understood from the following text.